Experimenting With The Chemistry of Fall Colors For National Chemistry Week

Using chemistry to find the colors hidden in leaves. Image: Kathy Ceceri

Here in my corner of North America the fall colors have finally started to emerge. And as I was admiring the reds, oranges, and yellows of the mountains surrounding my area, I was reminded of a cool experiment the kids and I did a couple years ago when we were studying chemistry. This week is also National Chemistry Week, so it’s a perfect time for trying a little chemistry at home.

What we did was take the organic solvent acetone — also known as nail polish remover — and use it to analyze the chemical composition of leaves from a variety of trees in our yard using a process called paper chromatography. Here’s how it works, according to Wikipedia:

The paper is placed in a jar containing a shallow layer of solvent and sealed. As the solvent rises through the paper, it meets the sample mixture which starts to travel up the paper with the solvent. This paper is made of cellulose, a polar substance, and the compounds within the mixture travel farther if they are non-polar. More polar substances bond with the cellulose paper more quickly, and therefore do not travel as far.

In the fall, the chlorophyll that gives tree leaves their green color slowly breaks down, and different colors of chlorophyll emerge. For our experiment, we took green leaves and drew out the different colored pigments. Then we compared the colors that emerged with the colors we saw in leaves that had already turned. The process was simple:

Find some green leaves from different kinds of trees. Also collect leaves that have already changed color, if possible.

For each type of leaf you’re testing, you’ll need a tall, clean, narrow jar; a pencil; a strip of absorbent paper (we used paper towels, but you can also try coffee filters or real chromatography paper); and a piece of tape.

Chop and/or mash up the green leaves. (We tore them, but you could be more scientific and use a food processor to get a more uniform mixture.)

Put each type of chopped-up leaf in its own jar.

Pour in enough acetone to cover the leave mixture.

For each jar, take a long strips of paper and tape it to a pencil so it hangs down.

Place one pencil across the top of each jar so the bottom of the paper is touching the acetone/leaf mixture. There should be at least 6 inches of paper above the liquid.

Let sit several hours or overnight.

Within a few hours, you should start to see horizontal stripes of different colored chlorophyll start to form. Look closely to see if you can find the colors of the falls leaves on your paper! You can find more chemistry activities to do with your kids at the American Chemistry Society’s website and at my blog Home Chemistry.